Tag Archives: technology

I work in nanoscience, and a lot of new materials and devices are developed where people ask, what is going to be the application of this? Can this displace an established technology (like silicon computer chips) or create a new market? And I was recently reminded of a great quote in response:

The principal applications of any sufficiently new and innovative technology always have been—and will continue to be—applications created by that technology.

That was said by Herbert Kroemer in his Nobel lecture, and it bears thinking about in many contexts both within science and in the broader world. When you’re doing something new, it may not fit neatly into the established hierarchies of technology, science, or industry. That can be good, and in fact it can be groundbreaking, like a present you didn’t know you wanted! Of course, it’s still important to think about how your work fits into the broader picture as it already is, but I think it’s always good to get a reminder to check your premises, that innovation can create its own new niches.

Last time when we talked about CCDs, we were concerned with how to take an optical signal, like an image, and convert it to an electronic signal. Then it can be processed, moved, and stored using electronics. But there is an obvious question this idea raises: why is the conversion to electronic signal needed? Why can’t we process the optical signal directly? Is there a way to manipulate a stream of photons that’s analogous to the way that electronic circuits manipulate streams of electrons?

The answer is yes, and the field dealing with optical signal processing is called photonics. In the same way that we can generate electronic signals and manipulate them, signals made up of light can be generated, shuffled around, and detected. While the underlying physical mechanisms are different from those in electronics, much of the same processing can take place! There are a lot of cool topics in photonics, but let’s go over some of the most basic technology just to get a sense for how it all works.

The most common way to generate optical signals in photonics is by using a laser diode, which is actually another application of the p-n junction. Applying a voltage across the junction itself causes electrons to drift into the junction from one side, while holes (which are oppositely charged) drift in from the other side. This “charge injection” results in a net current flow, but it also means that some electrons and holes will meet in the junction. When this happens, they can recombine if the electron falls into the empty electron state that the hole represents. But there is generally an energy difference between the free electron and free hole state, and this energy can then be emitted as a photon. This is how light with a specific energy is generated in the semiconductor laser diode, and when the junction is attached to an enclosed area to amplify that light, you get a very reliable light source that is easy to modulate in order to encode a signal.

But how do you send that signal anywhere else? Whereas electronic signals pass easily through metal wires, photonic signals are commercially transmitted through transparent optical fibers (hence the term “fiber optic”). Optical fibers take advantage of total internal reflection, a really cool phenomenon where for certain angles at an interface, all incident light is reflected off the interface. Since light is a quantized electromagnetic wave, how it moves through its surroundings depends on how easy it is to make the surrounding medium oscillate. Total internal reflection is a direct consequence of Snell’s Law, which describes how light changes when it goes between media that are not the same difficulty for light to pass through (the technical term for this is refractive index). So optical fibers consist of a fiber with high refractive index which is clad in a sheath with lower refractive index, tuned so that the inner fiber will exhibit total internal reflection for a specific wavelength of light. You can see an example of total internal reflection below, for light travelling through a plastic surrounded by air. When optical fibers exhibit total internal reflection, they can transmit photonic signals over long distances, with less loss than an electronic signal moving through a long wire would experience, as well as less susceptibility to stray electromagnetic fields.

Photonic signals can then be turned back into electronic signals using semiconducting photodetectors, which take advantage of the photoelectric effect. This technology is the basis of most modern wired telecommunications, including the Internet!

But if you are remembering all the electronic components, like resistors and capacitors and transistors, which we use to manipulate electronic signals, you may be wondering what the corresponding parts are for photonics. There are photonic crystals, which have microstructure that affects the passage of light, of which opal is a naturally occurring example! And photonic signals can be recorded and later read out on optical media like CDs and DVDs. But in general, the commercial possibilities of optical data transmission have outweighed those of complex photonic signal analysis. That’s why our network infrastructure is photonic but our computers, for now, are electronic. However, there are lots of researchers working in this area, so that could change, and that also means that if you find photonics interesting there is much more to read!

You may have noticed one big technology missing from my recent post on how displays work: I didn’t talk about plasma displays! I wanted to have more space to discuss what plasma actually is before getting into the detail of how the displays work, and that’s what today’s post is about.

Plasmas are usually considered a state of matter. But whereas order and density distinguish the other states of matter from each other—solids are dense and ordered, liquid are dense and disordered, and gases are disperse and disordered—for plasma there is another factor that is important. Plasmas are disperse and disordered like gases, but they are also ionized. Whereas a non-ionized gas consists of atoms, in an ionized gas the negatively charged electrons have been stripped from the positively charged atomic nuclei and both are moving freely through the gas. The electrons and nuclei are both called ions, to indicate that they carry a charge. Remembering the attractive force that oppositely charged particles experience, it might seem like a plasma would be pretty short-lived! Electrons and nuclei form stable atoms together because that is a low-energy configuration, which means it’s very appealing for the plasma to recombine into regular atoms. And in fact that’s what happens if you let it cool down, but if you keep the plasma temperature high, the ions are more likely to stay separated. In fact, how many of the atoms are ionized depends roughly on the plasma temperature. Hotter plasmas often have nearly all of their atoms broken apart and ionized, whereas cooler plasmas may be only partly ionized. But the more ions you have, the more electromagnetic interactions occur within the plasma because of all the free charge, and this is what makes plasmas behave differently from non-ionized gases.

A hot gas of ions may sound somewhat removed from the quotidian phases of solid, liquid, and gas. But actually, plasma is the most common phase of luminous matter in the universe, prevalent both in stars and in the interstellar medium. (I say luminous matter here to distinguish from dark matter, which seems to make up more total mass than the matter we can see, and whose phase and nature are both unknown.) There are also lots of examples of plasmas here on Earth, such as lightning bolts, the northern lights, and the neon that lights up a neon sign. You may have noticed that these are all light-emitting phenomena; the high energy of the ions means that they have many lower energy states available to jump to, and those energy level changes often involve emitting a photon to produce visible light.

So how can plasma be controlled to make a display? Illumination comes from tiny pockets of gas that can be excited into a plasma by applying an electrical current, and each pixel is defined by a separate plasma cell. For monochrome displays, the gas can be something like neon which emits light that we can see. But to create multiple colors of light, various phosphors are painted in front of the plasma cells. The phosphors absorb the light emitted by the plasma and emit their own light in a variety of colors (this is also how color CRT displays work). Plasma displays tend to have better contrast than LCDs and less dependence on viewing angle, but they also consume quite a bit of energy as you might expect from thinking about keeping the ions in the plasma separated.

There are a lot of other cool things about plasmas, like how they can be contained by electromagnetic fields and how they are used in modern industrial processing to etch semiconductors and grow nanomaterials. But for further reading I definitely recommend the wikipedia article on plasmas.

Edutainment can be a dirty word, depending on who you ask. While the blending of entertainment and education seems to be a positive step – why wouldn’t you want people to enjoy learning? – it can be viewed with distaste by those who consider themselves ‘real’ educators. Very few of them would claim that their own flavours of educational work are without enjoyment, so why this disconnect?

Edutainment centres around the idea that all learning should be ‘fun’, and often incorporates technology including video games, films and radio, often with an interactive focus. It’s informal and revolves less around a central teacher figure and more around the engagement of the student with a narrative designed to impart information while it also engages with them emotionally. And while edutainment principles can be used to deliver any curriculum, it often seems to be focused on making science fun and enjoyable for otherwise unengaged students.

The benefits of this type of engagement are myriad: it addresses the challenge of catching and keeping peoples’ attention, it can make traditionally ‘boring’ or ‘difficult’ subjects more engaging, and it does so in a way that requires little in the way of preparation or resources for those delivering it (after initial development, of course). So what objections could possibly be lodged against it?

One of the main criticisms seems to boil down to the fact that in ‘making learning fun’ traditional learning is relegated to the ‘unfun’ sector; it becomes an obstacle to cover up or transmute into something palatable and shiny. While scientists and engineers hopefully enjoy their jobs and are passionate about their subjects it’s doubtful than any given individual would agree that their progression and learning had been all fun, all the time. Should we be encouraging young people to engage only with that which tells them a nice story or catches their eye with well-designed graphics, or should we level with them that STEM isn’t always fun? Facts need to be learned, abstract theories must be understood, and above all critical thinking and hard work and dedication are key to becoming successful learners and contributors to the wider sphere of understanding.

That being said, as educators we should be willing to see our methods evolve and change with time. Edutaintment activities can have value as long as they are vetted and evaluated for impact (both on attitude and uptake of content) properly. Some developing technologies are especially exciting – for example, http://www.teachwithportals.com/ is a free-for-schools initiave launched by distribution platform Steam, allowing teachers to use the Puzzle Maker and other templates to explore physics, maths, technology and even literacy topics while students play their way through derivatives of a wildly popular video game. This will not be a solution for all – there comes the problem of timetable integration, of whether school computers are capable of running the appropriate software, of the training of teachers to make use of yet another new tool – but it might work for some. And if it doesn’t, well, there’s always the classics:

Now that we have started out with atoms and gone all the way to electronic band theory, which uses available energy states to explain why some materials are good at conducting electrons and others are not, we can start to discuss actual electronic devices! After all, fancy materials aren’t much good unless you have some way to use them.

Broadly speaking, we want devices that do something worthwhile, like light a room, make calculations, or power a motor. Most electrical devices work by manipulating a flow of electrons to extract some useful behavior. If we apply an electrical potential (which is also called voltage) to a device, then it will be energetically favorable for electrons to move through the device; this charge flow is called electrical current. The potential difference is often provided by something like a battery, where the differing chemical potential within the battery provides the voltage, and the device itself is connected to both terminals of the battery. Connecting a device to a battery forms a physical loop that electrons travel through, hence the name circuit. The battery itself is a circuit element, and so is the device that does something useful. There are quite a few interesting circuit elements but let’s start simple.

While the high electrical conduction of metals is extremely useful, sometimes it can be useful to have something that does not conduct electrons quite so well. Why? Because poor conductors offer the opportunity to convert electrical energy into other forms of energy, such as light or heat. This is the idea behind resistors, circuit elements that resist the flow of electrons without quite stopping it. Some resistor materials convert excess energy into heat, which can be the basis of electric heaters or electric stovetops. And the filament in an incandescent light bulb is acting as a resistor, one which heats up so much that it emits light (the reason for this is a whole other sack of beans). Resistors can be made by combining a conductive material with a non-conductive material, and are manufactured across an incredibly broad range of resistances. And independent of their heating or light-emitting properties, they are often used because the electrical current through them depends linearly on voltage.

And what happens if we push resistance to its limit, such that no electrons can actually pass through an insulating device? Applying a voltage drop would cause electrons to build up on one side of the device, attempting to pass through, until the repulsive force from the assembled electrons was enough to deter additional electrons from building up. The charge imbalance creates an electric field across the device, and this is what we call a capacitor. You can build a capacitor by bringing two parallel conducting plates close to each other and applying voltage. Since current can’t cross the gap between the plates, charge is stored on the capacitor plates, which can be discharged upon connection to a circuit. This is somewhat similar to a battery, although most batteries have stored chemical energy rather than electrical, and the speed of the chemical reaction which discharges a battery is usually much slower than the speed of electrons rushing to equilibrium when a capacitor is discharged. An older example of a capacitor is shown below; modern capacitors use thin films to create an insulating gap, and are considerably smaller than the capacitor pictured.

Resistors and capacitors are two of the most basic pieces that you can put into a circuit, and two of the most widely used. But some of the more complicated elements are interesting as well, and we’ll get into those in the next few posts!